This invention relates to the fabrication of microminiature devices and, more particularly, to a charged-particle-beam lithographic method and apparatus adapted to directly write on a workpiece surface in a high-speed manner.
Various types of charged-particle-beam lithographic apparatus are known in the art. Such apparatus utilizing, for example, a single scanned electron beam has been widely used in the electronics industry as a practical tool for generating high-quality fine-featured integrated circuit masks.
Charged-particle-beam lithographic apparatus is also capable of exposing patterns directly on the surface of a workpiece such as a resist-coated semiconductor wafer. But, in practice, such direct-writing apparatus has not been widely accepted for commercial production because of the relatively long time required to write patterns on a large-area wafer.
Efforts have been directed at trying to devise ways of increasing the pattern-writing speed of charged-particle-beam lithographic apparatus. The primary motivation for these efforts is the desire to increase the throughput of the apparatus. In that way, the cost per unit area exposed by the scanning beam would be reduced and the economic attractiveness of the apparatus as a production-worthy lithographic tool would be enhanced.
A number of techniques have been suggested for increasing the writing speed of charged-particle-beam lithographic apparatus. Thus, for example, as described in U.S. Pat. No. 4,393,312 issued to R. J. Collier and M. G. R. Thomson, the pattern-writing speed of such apparatus is increased by utilizing a mode of raster scanning in which the dimensions of a single writing spot are varied in a high-speed way during the scanning process. Other suggested ways of increasing writing speed involve expanding the output of a small-area source of charged particles by means of a linear or two-dimensional lens array to provide multiple writing spots, as described, for example, in U.S. Pat. No. 4,153,843 issued to R. F. W. Pease, and in "A Multiple-Electron-Beam Exposure System for High-Throughput, Direct-Write Submicrometer Lithography," By I. Brodie et al, IEEE Transactions on Electron Devices, Vol. ED-28, No. 11, November 1981, pages 1422-1428.
But none of the techniques suggested to date has in practice sufficiently increased writing speed to make charged-particle-beam lithographic apparatus economically attractive for general-purpose production use when operated in its direct-writing mode. Hence, efforts have continued by skilled workers in the art directed at trying to devise substantially faster ways of operating such apparatus. It was recognized that such efforts, if successful, had the potential for making the apparatus suitable for direct-writing production purposes. In turn, the availability and use of high-throughput apparatus characterized by very high resolution and excellent depth-of-focus properties would make it feasible to fabricate extremely high-quality fine-featured integrated circuits in an advantageous low-cost way.